Flat panel electron beam displays comprise a cathode and an anode contained in an evacuated envelope. In operation, the cathode is held at a negative potential relative to the anode. Electrons are emitted from the cathode. The potential difference between the cathode and the anode accelerates the emitted electrons from the cathode towards the anode. This is formed, within the display, into a beam. A beam current thus flows between the anode and the cathode. In flat panel electron beam displays a matrix arrangement is disposed between the cathode and the anode. The matrix arrangement is formed by a pair of "combs" placed at right angles to each other. These are commonly referred to as rows and columns. Each pixel or subpixel lies at the intersection of a row and a column. Each of the combs has many separate elements (rows or columns). In operation, a control voltage is applied to each element of each of the combs. The control voltage applied to each element imposes an electrostatic force on the electron beam associated with that element. The electron beam current associated with that element can be adjusted by adjusting the control voltage.
Matrix driven flat CRT displays require the use of an area cathode to provide a uniform source of electrons to each pixel aperture. Thermionic cathodes can be used, but these require heating to obtain emission, with its consequent problems of power dissipation and thermal management for the other parts of the flat CRT display. Field emission electron sources such as MIMs, PFEs and FEDs do not require heating, but are non space charge limited and suffer from problems of uniformity and instability that require some form of smoothing to make their use practical.